464 research outputs found
A Comparison of the Ovulation Method With the CUE Ovulation Predictor in Determining the Fertile Period
The purpose of this study was to compare the CUE Ovulation Predictor with the ovulation method in determining the fertile period. Eleven regularly ovulating women measured their salivary and vaginal electrical resistance (ER) with the CUE, observed their cervical-vaginal mucus, and measured their urine for a luteinizing hormone (LH) surge on a daily basis. Data from 21 menstrual cycles showed no statistical difference (T= 0.33, p= 0.63) between the CUE fertile period, which ranged from 5 to 10 days (mean = 6.7 days, SD = 1.6), and the fertile period of the ovulation method, which ranged from 4 to 9 days (mean = 6.5 days, SD = 2.0). The CUE has potential as an adjunctive device in the learning and use of natural family planning methods
Deformation of a nearly hemispherical conducting drop due to an electric field: theory and experiment
We consider, both theoretically and experimentally, the deformation due to an electric field of a pinned nearly-hemispherical static sessile drop of an ionic fluid with a high conductivity resting on the lower substrate of a parallel plate capacitor. Using both numerical and asymptotic approaches we find solutions to the coupled electrostatic and augmented Young–Laplace equations which agree very well with the experimental results. Our asymptotic solution for the drop interface extends previous work in two ways, namely to drops that have zero-field contact angles that are not exactly π/2 and to higher order in the applied electric field, and provides useful predictive equations for the changes in the height, contact angle and pressure as functions of the zero-field contact angle, drop radius, surface tension and applied electric field. The asymptotic solution requires some numerical computations, and so a surprisingly accurate approximate analytical asymptotic solution is also obtained
Probing Pseudogap by Josephson Tunneling
We propose here an experiment aimed to determine whether there are
superconducting pairing fluctuations in the pseudogap regime of the high-
materials. In the experimental setup, two samples above are brought into
contact at a single point and the differential AC conductivity in the presence
of a constant applied bias voltage between the samples, , should be
measured. We argue the the pairing fluctuations will produce randomly
fluctuating Josephson current with zero mean, however the current-current
correlator will have a characteristic frequency given by Josephson frequency
. We predict that the differential AC conductivity
should have a peak at the Josephson frequency with the width determined by the
phase fluctuations time.Comment: 4 pages, 2 eps figure
Transport properties of heterogeneous materials derived from Gaussian random fields: Bounds and Simulation
We investigate the effective conductivity () of a class of
amorphous media defined by the level-cut of a Gaussian random field. The three
point solid-solid correlation function is derived and utilised in the
evaluation of the Beran-Milton bounds. Simulations are used to calculate
for a variety of fields and volume fractions at several different
conductivity contrasts. Relatively large differences in are observed
between the Gaussian media and the identical overlapping sphere model used
previously as a `model' amorphous medium. In contrast shows little
variability between different Gaussian media.Comment: 15 pages, 14 figure
Antiferromagnetism from phase disordering of a d-wave superconductor
The unbinding of vortex defects in the superconducting condensate with d-wave
symmetry at T=0 is shown to lead to the insulator with incommensurate
spin-density-wave order. The transition is similar to the spontaneous
generation of the "chiral" mass in the three dimensional quantum
electrodynamics, at which the global chiral symmetry one can define in the
superconducting state is spontaneously broken. Other symmetry related states
and possible relations to recent experiments on uderdoped cuprates are briefly
discussed.Comment: RevTex, 4 pages, one ps figure; comments on confinement in the SDW
added, references updated; final versio
Phase-fluctuation induced reduction of the kinetic energy at the superconducting transition
Recent reflectivity measurements provide evidence for a "violation" of the
in-plane optical integral in the underdoped high-T_c compound
Bi_2Sr_2CaCu_2O_{8+\delta} up to frequencies much higher than expected by
standard BCS theory. The sum rule violation may be related to a loss of
in-plane kinetic energy at the superconducting transition. Here, we show that a
model based on phase fluctuations of the superconducting order parameter can
account for this change of in-plane kinetic energy at T_c. The change is due to
a transition from a phase-incoherent Cooper-pair motion in the pseudogap regime
above T_c to a phase-coherent motion at T_c.Comment: 5 pages, 3 eps-figure
Magnetic field induced charge and spin instabilities in cuprate superconductors
A d-wave superconductor, subject to strong phase fluctuations, is known to
suffer an antiferromagnetic instability closely related to the chiral symmetry
breaking in (2+1)-dimensional quantum electrodynamics (QED3). On the basis of
this idea we formulate a "QED3 in a box" theory of local instabilities of a
d-wave superconductor in the vicinity of a single pinned vortex undergoing
quantum fluctuations around its equilibrium position. As a generic outcome we
find an incommensurate 2D spin density wave forming in the neighborhood of a
vortex with a concomitant "checkerboard" pattern in the local electronic
density of states, in agreement with recent neutron scattering and tunneling
spectroscopy measurements.Comment: 4 pages REVTeX + 2 PostScript figures included in text. Version to
appear in PRL (minor stylistic changes, references updated). For related work
and info visit http://www.physics.ubc.ca/~fran
Induced local spin-singlet amplitude and pseudogap in high cuprates
In this paper we show that local spin-singlet amplitude with d-wave symmetry,
, can be induced by short-range spin correlations even
in the absence of pairing interactions. Fluctuation theory is formulated to
make connection between pseudogap temperature $T^{*}$, pseudogap size
$\Delta_{pg}$ and . In the present scenario for the
pseudogap, the normal state pseudogap is caused by the induced local
spin-singlet amplitude due to short-range spin correlations, which compete in
the low energy sector with superconducting correlations to make go to
zero near half-filling. Calculated falls from a high value onto the
line and closely follows mean-field N\'{e}el temperature .
The calculated is in good agreement with experimental results. We
propose an experiment in which the present scenario can be critically tested.Comment: 5 pages, 3 figure
Optical monitoring of the gravitationally lensed quasar Q2237+0305 from APO between June 1995 and January 1998
We present a data set of images of the gravitationally lensed quasar
Q2237+0305, that was obtained at the Apache Point Observatory (APO) between
June 1995 and January 1998. Although the images were taken under variable,
often poor seeing conditions and with coarse pixel sampling, photometry is
possible for the two brighter quasar images A and B with the help of exact
quasar image positions from HST observations. We obtain a light curve with 73
data points for each of the images A and B. There is evidence for a long (>~
100 day) brightness peak in image A in 1996 with an amplitude of about 0.4 to
0.5 mag (relative to 1995), which indicates that microlensing has been taking
place in the lensing galaxy. Image B does not vary much over the course of the
observation period. The long, smooth variation of the light curve is similar to
the results from the OGLE monitoring of the system (Wozniak et al. 2000a).Comment: 8 pages, 5 figures; accepted for publication in A&
Algebraic Fermi liquid from phase fluctuations: "topological" fermions, vortex "berryons" and QED3 theory of cuprate superconductors
Within the phase fluctuation model for the pseudogap state of cuprate
superconductors we identify a novel statistical "Berry phase" interaction
between the nodal quasiparticles and fluctuating vortices. The effective action
describing this model assumes the form of an anisotropic Euclidean quantum
electrodynamics in (2+1) dimensions (QED_3) and naturally generates the
marginal Fermi liquid behavior for its fermionic excitations. The doping axis
in the x-T phase diagram emerges as a quantum critical line which regulates low
energy fermiology. We examine the merits of our theory in light of available
experiments.Comment: 5 pages REVTeX + 2 PostScript Figures. Final version to appear in PR
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